I see you did not post your /etc/amavis/conf.d/15-av_scanners file, you need to uncomment clamav there otherwise no scanner will run for you I guess.
It should look something like this :
['ClamAV-clamd',
\&ask_daemon, ["CONTSCAN {}\n", "/var/run/clamav/clamd.sock"],
qr/\bOK$/, qr/\bFOUND$/,
qr/^.*?: (?!Infected Archive)(.*) FOUND$/ ],
-- Yassine
